Method and electrolyte for electroplating rhodium-rhenium alloys

ABSTRACT

Disclosed is an electroplating bath suitable for depositing a rhodium-rhenium alloy containing at least 70 weight % rhodium. Rhodium and rhenium are present in the plating bath in the form of soluble plateable compounds in a preferred weight ratio of at least about 4:1. The deposits obtained by this bath exhibit improved brightness over comparable baths containing no rhenium even without the addition of lead.

United States Patent [1 Stevens et al.

[ METHOD AND ELECTROLYTE FOR ELECTROPLATING RHODlUM-RHENIUM ALLOYS [75] Inventors: Peter Stevens, Parsippany; George R. Lurie, South Bound Brook, both of NJ.

[73] Assignee: Oxy Metal Industries Corporation,

Detroit, Mich.

[22] Filed: Sept. 20, 1974 [21] Appl. No.: 507,831

Related U.S. Application Data [63] Continuation-impart of Ser. No. 372376, June 21 1973, abandoned.

[52] U.S. Cl 204/43 N [51] Int. Cl C23b 5/32 [58] Field of Search 204/43 N, 45 R, 45.5, 47,

[ June 17, 1975 [56] References Cited OTHER PUBLICATIONS Abner Brenner, Electrodeposition of Alloys," Vol. ll, pp. 598-606, (1963).

Primary E.\'aminer-G. L. Kaplan Attorney, Agent, or Firm-Arthur E. Kluegel; Richard P. Mueller; Betram F. Claeboe 5 7 ABSTRACT I Disclosed is an electroplating bath suitable for deposabout 4:1. The deposits obtained by this bath exhibit improved brightness over comparable baths containing no rhenium even without the addition of lead.

7 Claims, No Drawings .1 METHOD AND ELECTROLYTE FOR ELECTROPLATING RHODlUM-RHENIUM ALLOYS,

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of U.S. Ser. No. 372,376 filed June 21, 1973, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to improvements in and relating to the electrodeposition of rhodium alloys.

Electrodeposited rhodium has found considerable favor in recent years as a decorative coating material and as a contact face material owing to its extreme hardness and its resistance to corrosion and tarnish. Under normal conditions, rhodium is substantially un affected by contact with common acids and chemicals.

Deposits of rhodium typically exhibit desirable characteristics with regard to resistance to corrosion and wear, and superior hardness coupled with exceptionally high resistance to heat and good electrical conductivity. These properties render the rhodium deposit useful not only as protective coatings for silverware and jewelry but also as protecting parts for electronic applications. The primary disadvantage of rhodium deposits is that they are somewhat lacking in desired brightness for certain applications.

U.S. Pat. No. 3,671,408 discloses a bath suitable for depositing a rhodium-platinum alloy. Both rhodium and platinum are classified as precious metals and the price of such metals is on the order of $55/oz. and upward. The present invention permits the plater to obtain brightened deposits of a predominately rhodium alloy without incorporating a Group VIII (b) precious metal.

U.S. Pat. No. 3,692,641 teaches a deposit containing ruthenium, rhodium and platinum. The deposit is predominately ruthenium and contains minor portions of rhodium or platinum. Additionally, the bath disclosed in that patent contains indium thallium or gallium elements of Group III (a) of the Periodic Table of Elements. Since the deposit of that patent contains only minor portions of rhodium, it does not exhibit the well known advantageous characteristics of a rhodium deposit. US. Pat. No. 3,31 1,547 likewise discloses a rhodium alloy deposit containing the Group III (a) element indium as the alloying metal. None of the foregoing patents disclose the use of rhenium as a brightener for rhodium deposits.

SUMMARY OF THE INVENTION It has now been discovered that a rhodium deposit of improved brightness can be obtained by including in the electroplating bath a minor quantity of a soluble rhenium compound. The bath is aqueous and acidic and contains a soluble rhodium compound and a compatible soluble rhenium compound in a weight ratio of rhodium to rhenium sufficient to deposit an alloy containing at least 70 weight rhodium.

DETAILED DESCRIPTION OF THE INVENTION The scope of the invention includes an electroplating bath, a method of electroplating comprising electrolyzing the bath, and the resulting plated article.

Since it is desired that the deposit exhibit to the extent possible the advantageous characteristics of a pure rhodium deposit, the deposit should be predominately rhodium. By predominately, we mean the deposit should contain at least weight rhodium. Preferably, the deposit will contain at least about weight rhenium and most preferably weight The rhenium content of the electroplating bath is dependent upon the rhodium concentration. The rhodium concentration may be between 0.1 and 15 grams per liter and preferably between 0.5 and 5 grams per liter. The desired rhenium content may vary somewhat depending on the presence and concentration of additive components and operating conditions such as current density but should be selected to provide a deposit of at least 70 weight rhodium. Under normal operating conditions specified below, the weight ratio of rhodium to rhenium is at least 4:1 and is preferably at least 10:1. Typically, the rhenium content will vary between and 200 mg/l.

The rhodium salts generally used for plating are rhodium sulfate, rhodium sulfamate or rhodium phosphate. However, any rhodium slat may be used which provides the rhodiumin a condition such that rhodium can be plated from an acid bath and which is stable under the acid conditions required.

The preferred rhenium compounds are the alkali metal and ammonium perrhenates and perrhenic acid. However, any rhenium salt suitable for plating rhenium may be substituted.

The bath should be maintained on the acid side by the presence of at least 10 g/l of a compatible strong inorganic acid. Preferably, the bath contains sulfamic acid in a concentration of from 10 g/l up to the solubility limit of the solution. Preferably, the sulfamic acid is present in a concentration between 20 and 150 grams per liter and most preferably between 50 and grams per liter.

The bath may additionally contain other additives well known in the art. Suitable additives include those for improving conductivity, providing buffering power, and complexing metallic ions. It has been found that concentrated sulfuric acid may be advantageously added to the present bath to improve the conductivity Normally quantities of up to 100 milliliters per liter of solution and preferably between 1 and 50 milliliters per liter of solution are satisfactory.

The rhodium-rhenium bath may be used to plate any base metal surface on which rhodium itself can be plated. Suitable base metals include brass, bronze, copper, silver, mild steel, nickel and nickel alloys. In some instances, it may be desirable to flash plate a layer of silver over the base metal prior to plating in order to avoid reaction between the base metal and the plating bath. Flash platings of palladium, palladium-gold or gold are also suitable for this purpose.

The rhodium-rhenium alloy may be deposited from the bath at a temperature of between about 60 and 180F. by passing the current at a current density of about 5 to 40 amps per square foot through the bath to a cathode immersed therein. Preferably, the current density is about 10 to 30 amps per square foot and the temperature about 80 to F.

The deposits obtained by the process of this invention range from flash coatings of approximately 2 micro inch thickness up to coatings of 200 micro inches or more. The advantage of the deposit of this invention lies in the fact that the brightness is superior to that of pure rhodium deposits known in the art.

EXAMPLE A bath was prepared containing the following ingredients per liter:

Rhodium as rhodium sulfate Sulfamic acid Concentrated sulfuric acid oom comm

The bath temperature was maintained between 110 and 120F. A current density of 20 amps/square foot was applied using a platinum anode and a brass panel. While the above concentrations were substantially maintained, plating was performed under agitation after adding rhenium in concentrations varying between approximately 0.01 and 0.15 g/l. The rhenium was added in the form of KReO In every case, the deposits obtained were bright. A titanium panel was plated and the deposit analyzed and found to contain between 10 and rhenium. Similar baths prepared without the rhenium or sulfamic acid produced no mirror bright deposits and most exhibited pitting in the deposits.

What is claimed is:

1. An aqueous acidic electroplating bath, suitable for depositing a bright rhodium-rhenium alloy consisting essentially of rhodium and rhenium comprising at least 10 g/l of sulfamic acid, from 0.1 to 15 g/l of rhodium as a plateable compound, and at least 0.01 g/l rhenium as a plateable compound in a weight ratio of rhodium to rhenium of at least 411.

2. The bath of claim 1 wherein said weight ratio is at least 10:1.

3. The bath of claim 1 wherein said rhenium concentration is from 0.1 to 0.2 g/l.

4. The bath of claim 1 comprising at least 10 ml/l of concentrated sulfuric acid and between about 50 and 100 g/l of sulfamic acid.

5. The bath of claim 1 wherein said rhodium compound is a salt selected from the group consisting of sulfate, sulfamate and phosphate and said rhenium compound is selected from the group consisting of the alkali metal and ammonium perrhenates and perrhenic acid.

6. A method of plating a rhodium-rhenium alloy deposit on a base metal surface comprising electrolyzing the surface in the presence of the bath of claim 1 with the base metal as a cathode.

7. The method of claim 6 wherein saidvbase metal is selected from the group consisting of brass, bronze,

copper, silver, mild steel, nickel and nickel alloys. 

1. AN AQUEOUS ACIDIC ELECTROPLATING BATH, SUITABLE FOR DEPOSITING A BRIGHT RHODIUM-RHENIUM ALLOY CONSISTING ESSENTIALLY OF RHODIUM AND THEMIUM COMPRISING AT LEAST 10 G/L OR SULFAMIC ACID, FROM 0.1 TO 15 G/L RHODIUM AS A PLATEABLE COMPOUND, AND AT LEAST 0.01 G/L RHENIUM AS A PLATEABLE COMPOUND IN A WEIGHT RATIO OF RHODIUM TO RHENIUM OF AT LEAST 4:2.
 2. The bath of claim 1 wherein said weight ratio is at least 10:
 3. The bath of claim 1 wherein said rhenium concentration is from 0.1 to 0.2 g/l.
 4. The bath of claim 1 comprising at least 10 ml/l of concentrated sulfuric acid and between about 50 and 100 g/l of sulfamic acid.
 5. The bath of claim 1 wherein said rhodium compound is a salt selected from the group consisting of sulfate, sulfamate and phosphate and said rhenium compound is selected from the group consisting of the alkali metal and ammonium perrhenates and perrhenic acid.
 6. A method of plating a rhodium-rhenium alloy deposit on a base metal surface comprising electrolyzing the surface in the presence of the bath of claim 1 with the base metal as a cathode.
 7. The method of claim 6 wherein said base metal is selected from the group consisting of brass, bronze, copper, silver, mild steel, nickel and nickel alloys. 